Could Fish Feeding Behaviour and Size Explain Prevalence Differences of the Nematode Eustrongylides excisus among Species? The Case Study of Lake Garda

The nematode Eustrongylides excisus is a parasite of freshwater fish- and fish-eating birds, with known differences on prevalence values among fish species. Thus, the present study aims to explore the hypothesis that the feeding behavior and the size of fish belonging to different trophic levels could explain such differences. For that, 14 sampling sites were selected to perform a fish parasitological survey on Lake Garda (Italy) during spring-summer 2020. Amplification of nuclear ribosomal internal transcribed spacer (ITS) rDNA sequences of nematodes morphologically ascribable to the genus Eustrongylides allowed to identify them as E. excisus. From the five studied fish species (Perca fluviatilis, Lepomis gibbous, Coregonus lavaretus, Alosa fallax lacustris and Micropterus salmoides), only three presented the parasite E. excisus: P. fluviatilis, L. gibbous and M. salmoides, with significant differences in prevalence values among species (p = 0.002). Additionally, there were differences in prevalence values within the same fish species captured from different sampling sites. Findings showed that mainly piscivorous fish were positive for E. excisus and how the prevalence was highest in M. salmoides. As regard the fish size, a negative correlation between body size and E. excisus was found in P. fluviatilis due to the feeding habit of juvenile perch which feed mainly zooplankton and benthic invertebrates (i.e., oligochaetes, which are the first intermediate hosts of E. excisus). The study findings advance novel knowledge in the field of pathogens of zoonotic importance in the aquatic environment.

Reconstructing the Gorte and Spiaz de Navesele Landslides, NE of Lake Garda, Trentino Dolomites (Italy)

We applied a multi-method approach to reconstruct the Gorte rock avalanche (85–95 Mm3) located at the northeastern end of Lake Garda. The combination of field mapping, characterization of bedrock discontinuities, Dan3D-Flex runout modeling and dating of boulders with cosmogenic 36Cl supports the conclusion that the deposits stem from a single rock avalanche at 6.1 ± 0.8 ka. The Gorte event may have triggered the Spiaz de Navesele–Salto della Capra landslide (3.2 Mm3), whose deposits cover the southern end of the Gorte deposits. First-order controls on detachment were the NNE–SSW- and WNW–ESE-oriented fractures in the limestone bedrock, related to the Giudicarie and Schio-Vicenza fault systems, respectively. Dan3D-Flex runout modeling sufficiently reproduced the Gorte rock avalanche, which involved detachment and sliding of a quasi-intact block, likely along marly interbeds, followed by rapid disintegration. The frictional rheology in the source area and the turbulent frictional rheology (Voellmy) in the remaining part best replicate the observed deposit extent and thickness. Heavy precipitation that occurred at that time may have contributed to failure at Gorte. Nonetheless, its timing overlaps with the nearby (<15 km) Dosso Gardene (6630–6290 cal BP) and Marocca Principale (5.3 ± 0.9 ka) landslides, making a seismic trigger plausible.

A multi-site, year-round turbulence microstructure atlas for the deep perialpine Lake Garda

A multi-site, year-round dataset comprising a total of 606 high-resolution turbulence microstructure profiles of shear and temperature gradient in the upper 100 m depth is made available for Lake Garda (Italy). Concurrent meteorological data were measured from the fieldwork boat at the location of the turbulence measurements. During the fieldwork campaign (March 2017-June 2018), four different sites were sampled on a monthly basis, following a standardized protocol in terms of time-of-day and locations of the measurements. Additional monitoring activity included a 24-h campaign and sampling at other sites. Turbulence quantities were estimated, quality-checked, and merged with water quality and meteorological data to produce a unique turbulence atlas for a lake. The dataset is open to a wide range of possible applications, including research on the variability of turbulent mixing across seasons and sites (demersal vs pelagic zones) and driven by different factors (lake-valley breezes vs buoyancy-driven convection), validation of hydrodynamic lake models, as well as technical studies on the use of shear and temperature microstructure sensors.

Deep-mixing and deep-cooling events in Lake Garda: Simulation and mechanisms

A calibrated three-dimensional numerical model (Delft3D) and in-situ observations are used to study the relation between deep-water temperature and deep mixing in Lake Garda (Italy). A model-observation comparison indicates that the model is able to adequately capture turbulent kinetic energy production in the surface layer and its vertical propagation during unstratified conditions. From the modeling results several processes are identified to affect the deep-water temperature in Lake Garda. The first process is thermocline tilting due to strong and persistent winds, leading to a temporary disappearance of stratification followed by vertical mixing. The second process is turbulent cooling, which acts when vertical temperature gradients are nearly absent over the whole depth and arises as a combination of buoyancy-induced turbulence production due to surface cooling and turbulence production by strong winds. A third process is differential cooling, which causes cold water to move from the shallow parts of the lake to deeper parts along the sloping bottom. Two of these processes (thermocline tilting and turbulent cooling) cause deep-mixing events, while deep-cooling events are mainly caused by turbulent cooling and differential cooling. Detailed observations of turbulence quantities and lake temperature, available at the deepest point of Lake Garda for the year 2018, indicate that differential cooling was responsible for the deep-water cooling at that location. Long-term simulations of deep-water temperature and deep mixing appear to be very sensitive to the applied wind forcing. This sensitivity is one of the main challenges in making projections of future occurrences of episodic deep mixing and deep cooling under climate change.

Monitoring Lakes Surface Water Velocity with SAR: A Feasibility Study on Lake Garda, Italy

The SAR Doppler frequencies are directly related to the motion of the scatterers in the illuminated area and have already been used in marine applications to monitor moving water surfaces. Here we investigate the possibility of retrieving surface water velocity from SAR Doppler analysis in medium-size lakes. ENVISAT images of the test site (Lake Garda) are processed and the Doppler Centroid Anomaly technique is adopted. The resulting surface velocity maps are compared with the outputs of a hydrodynamic model specifically validated for the case study. Thermal images from MODIS Terra are used in support of the modeling results. The surface velocity retrieved from SAR is found to overestimate the numerical results and the existence of a bias is investigated. In marine applications, such bias is traditionally removed through Geophysical Model Functions (GMFs) by ascribing it to a fully developed wind waves spectrum. We found that such an assumption is not supported in our case study, due to the small-scale variations of topography and wind. The role of wind intensity and duration on the results from SAR is evaluated, and the inclusion of lake bathymetry and the SAR backscatter gradient is recommended for the future development of GMFs suitable for lake environments.

New Leptogamasus mite species (Parasitiformes: Parasitidae) from Europe. II. Northern Italy

The four new species belonging to Parasitidae family, Leptogamasus (Leptogamasus) bicornis n. sp., Leptogamasus (L.) digiticornis n. sp., Leptogamasus (L.) sextus n. sp. and Leptogamasus (L.) trentinis n. sp. originating from the surroundings of Lake Garda (Lago di Garda), northern Italy, are described.

Deep-mixing and deep-cooling events in Lake Garda: Simulation and Mechanisms

&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;A calibrated three-dimensional numerical model&amp;#160;&lt;span&gt;(Delft3D) and in-situ observations are used to study the relation between deep water temperature and mixing in Lake Garda (Italy). A model-observation comparison indicates that the model is able to adequately capture the production of turbulent kinetic energy in the surface layer and its vertical propagation during unstratified conditions. Here, the model is used as a support to identify the main processes causing deep water cooling and deep mixing in the lake. The analysis indicated that two processes cause mixing over the entire depth. The first process is thermocline tilting due to strong and persistent winds. This is found to generate a temporary disappearance of stratification followed by vertical mixing over the entire depth. The second process is turbulent cooling, which arises as a combination of negative-buoyancy produced by surface cooling and turbulence injection from strong winds. Turbulent cooling acts when vertical temperature gradients are absent over the whole depth and cools and mixes the lake over its entire vertical. The third identified process is associated to differential&amp;#160;cooling between the shallow southern part and the deep northern trunk. This generates the advection of cold water from the southern, colder and well-mixed basin to the norther trunk along the sloping bottom of the lake. Such differential cooling is found to be a consequence of the turbulent cooling and is not associated with mixing over the entire depth in the northern trunk. Available observations indicate that the three processes identified from the model indeed occur in Lake Garda. Long- term simulations of deep water temperature and related deep mixing appear to be very sensitive to the atmospheric forcing,&amp;#160;whose accurate reproduction is essential for the prediction of the future occurrence of deep mixing events.&lt;/span&gt;&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt;